The invention relates to rubber bearings, and, more particularly, to a rubber bearing in which a liquid-filled working chamber is bounded at least by a resilient expanding member and by a compensating wall that is capable of moving back and forth in the direction of the working chamber. The compensating wall consists at least partially of a material that is capable of being moved by magnetic forces. One partial area of the compensating wall extends into an air gap between mutually opposing magnetic coils, which are rigidly supported in coil braces and are capable of receiving an electric alternating current.
The German Published Patent Application DE-OS 34 23 698 discloses a rubber bearing using a fluid chamber. This rubber bearing is also described in U.S. Pat. No. 4,650,170 to Fukushima, the disclosure of which is hereby incorporated by reference into the present specification. Pulsating pressure fluctuations are generated in the fluid contained in the fluid chamber of that bearing by a vibrational element activated by magnetic coils. If movement of the vibrational element is modulated in relation to vibrations introduced from the outside, then transmission of vibrations is reduced.
In the bearing described in DE-OS 34 23 698 and U.S. Pat. No. 4,650,170, the magnetic coils must be alternately triggered to isolate vibrations, since the coils can generate only attractive forces. Further, the attractive forces on the vibrational element are proportional to the square of the coil current, requiring special equalization measures to achieve a sinusoidal response. Moreover, because the forces vary significantly with the gap width, the system reacts quite sensitively to mechanical tolerance errors. Additionally, no precautions have been taken to retain the compensating wall in a neutral position symmetrically between the magnetic coils.